Cyclic topology exerts significant effects on the properties and potential applications of polymers; however
the precisely controlled systhesis of cyclic diblock copolymers remains challenging. In this study
we reported a novel and versatile synthetic strategy toward cyclic diblock copolymers by using the linear polymer precursors generated from reversible addition-fragmentation transfer (RAFT) polymerization. Key innovation of the technique proposed lies in the facile and complete conversion of terminal RAFT groups on linear polymers into clickable alkyne groups
via
a one-pot aminolysis/Michael addition reaction
which laid a foundation for subsequent intrachain Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) on the linear
α
-alkyne-
ω
-azide preursors. Full decoration of the RAFT termini was confirmed by Ellman study. Specifically
a cyclic double hydrophilic block copolymer (DHBC)
with thermo-responsiveness was synthesized following this approach successfully as confirmed by
1
H-NMR
13
C-NMR
FTIR
and SEC-MALLS analyses. Thermo-induced phase transitions and self-assembly behaviors of the resulting cyclic DHBCs were then investigated by the combined analytical techniques of UV-Vis spectroscopy
dynamic light scattering (DLS)
and transmission electron microscopy (TEM)
and further compared with those of the linear analogues. Intriguingly
the cyclic thermo-sensitive DHBCs exhibited a lower critical solution temparature (LCST
41.5 °C) significantly higher than the linear counterparts (39 °C)
for POEGMA moiety with two block juntions in the cyclic copolymers could raise the LCST of PNIPAAm segment. More importantly
the spherical micelles self-assembled from cyclic DHBCs above LCST were smaller in size and narrower in size distribution compared with the ones derived from linear analogues
which resulted most likely from a more restricted cyclic topology. This study therefore developed an efficient alternative synthetic method for cyclic diblock copolymers and meanwhile provided new insights into the structure-property relationships of cyclic DHBCs.
关键词
环状聚合物温敏性双亲性嵌段共聚物较低临界溶解温度
Keywords
Cyclic polymerThermo-sensitivityDouble hydrophilic block copolymerLower critical solution temperature
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Related Author
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Related Institution
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University
State Key Laboratory of Fine Chemicals, Dalian University of Technology
School of Chemistry and Chemical Engineering, Key Laboratory of Environment-friendly Polymer Materials of Anhui Province, Anhui University
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Department of College of Chemistry and Molecular Engineering, Peking University